add fs_util module with a few useful functions for file/path management

src/fs_util.rs

@@ -0,0 +1,22 @@
+use std::path::{Path, PathBuf};
+
+/// Ensures the given path exists by creating it if it doesn't.
+pub fn ensure_path_exists(path: &PathBuf) -> anyhow::Result<()> {
+    if !path.exists() {
+        debug!("Path {:?} doesn't exist, creating it", path);
+        std::fs::create_dir_all(path)?;
+    }
+    Ok(())
+}
+
+/// Joins a parent folder and a sub-path, resolving the subpath beforehand to ensure that
+/// the resulting path is still within the parent folder, regardless of ".." in the sub-path.
+pub fn join_path_secure(parent: &Path, sub: &Path) -> anyhow::Result<PathBuf> {
+    Ok(parent.join(sub.canonicalize()?.as_path()))
+}
+
+/// Converts a PathBuf into a String in a lossy way. This is generally the way we want to do it
+/// in the server.
+pub fn path_to_string(path: PathBuf) -> String {
+    path.into_os_string().to_string_lossy().to_string()
+}